1. Field of the Invention
The present invention relates to a channel selection mechanism, and more particularly, to a method of determining a channel map according to power spectrum density (PSD) and an apparatus thereof.
2. Description of the Prior Art
For a wireless communications system, there are a variety of interference sources in the air, e.g. the interference from the background, the interference from electronic device(s), the interference from the same transmission band, the interference from adjacent transmission band(s), and/or the interference from other wireless communications system(s). Thus, a wireless router or abase station is generally configured to operate in a transmission band with less interference, to thereby have better transmission efficiency.
For example, PSD is an index used to judge the energy scale of each band in the view of the spectrum, and can be used to determine the interference. In general, when the PSD value of a band is larger, it means that there is data transmission or interference source in the band. Please refer to FIG. 1, which shows an example of a conventional power spectrum density distribution. In FIG. 1, a threshold TH is used as a criterion for determining whether the PSD of a channel is too high. When the PSD of a channel exceeds the threshold TH, the channel will be viewed as a bad channel. That is, there is an interference source in the channel. Therefore, the bands with interference can be found through the power spectrum density detection technique. Next, the communications system avoids using these bad channels to improve the communications quality.
However, in order to reduce the cost of hardware, the PSD detection is usually performed by using the radio-frequency (RF) circuit of the communications apparatus, which makes the communications apparatus unable to perform data transmission. In other words, to achieve both of good communications quality and good transmission efficiency, the PSD detection has to be performed only in the period that the communications apparatus does not perform data transmission. Thus, the number of times of performing PSD detection is limited due to limited time periods. Besides, since the interference signals may appear or disappear with time, the PSD detection result might not exactly reflect the power spectrum density of the interference signals.
Thus, there is a need for a channel selection method which allows the PSD detection technique to correctly determine the bands with interference in a wireless local area network (WLAN), so as to improve the transmission quality and transmission rate by avoiding these bands with interference.